Rigid disk magnetic storage units have little tolerance for particulate matter that is present in the atmosphere within the sealed head-disk enclosure. With heads that fly above the data surface at 15 microinches, a one micron particle is three times the distance separating the head and disk surface and will result in a head crash, damage to the disk surface or both. As data areal densities are increased, this problem becomes progressively more acute as the magnetic coatings become thinner and more fragile and the head is required to fly closer and closer to the disk surface. Although the drive is assembled and sealed in a clean room, it is necessary to scavenge the residual contamination and continue to filter from the atmosphere any particulate contamination that may be generated within the enclosure during the life of the device.
Frequent air changes through a filter capable of removing damaging particulate matter are necessary to maintain an atmosphere that can sustain error free operation. This is increasingly difficult to achieve as the number of disks is increased, the electronic control is enhanced and the overall dimensions of the file are effectively limited by the industry standard form factor.